title: Adsorption of antibiotic ciprofloxacin on carbon nanotubes: pH dependence and thermodynamics.
abstract: The environmental risks of antibiotics have attracted increasing research attention, but their environmental behaviors remain unclear. In this study, functionalized carbon nanotubes (CNTs), namely, hydroxylized (MH), carboxylized (MC), graphitized multi-walled CNTs (MG) and single-walled CNTs (SW) were used as adsorbents and ciprofloxacin (CIP) as an adsorbate to investigate the effect of pH and temperature on sorption and desorption processes. Sorption isotherms of CIP were fitted well by Freundlich and Dubinin-Ashtakhov models. Highly nonlinear isotherms of CIP were observed, indicating the highly heterogeneous site energy distribution on CNTs. At all pHs, SW had the highest sorption for CIP due to its largest surface area among all CNTs. Sorption distinction between MH and MC was explained by π-π electron donor-acceptor interactions. For SW, CIP sorption was thermodynamically favorable and endothermic associated with an entropy driven process, while the reverse process occurred for MC and MG. The rearrangement of CNTs bundles/aggregates and covalent bond formation may be responsible for CIP desorption hysteresis on CNTs. Desorption of antibiotics from CNTs may lead to potential exposure, particularly under changing environmental conditions such as temperature and pH.
authors.affiliation: College of Plant Sciences, Jilin University of Agricultural Science & Technology, Jilin 132101, China; Stockbridge School of Agriculture, University of Massachusetts, Amherst, MA 01003, USA.
authors.forename: Haibo
authors.initials: H
authors.lastname: Li
authors.forename: Di
authors.initials: D
authors.lastname: Zhang
authors.forename: Xiaozeng
authors.initials: X
authors.lastname: Han
authors.forename: Baoshan
authors.initials: B
authors.lastname: Xing
mesh_terms: D000327:Adsorption; D000900:Anti-Bacterial Agents / Q000737:chemistry*; D002939:Ciprofloxacin / Q000737:chemistry*; D052918:Environmental Restoration and Remediation; D006863:Hydrogen-Ion Concentration; D008956:Models, Chemical; D037742:Nanotubes, Carbon / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D000900:Anti-Bacterial Agents; D037742:Nanotubes, Carbon; D002939:Ciprofloxacin
keywords: Antibiotics; Desorption hysteresis; Hydrophobicity; Nanotubes; Sorption energy